The present invention relates generally to plastic fasteners.
In U.S. Pat. No. 4,039,078 to A. R. Bone, which is incorporated herein by reference, there are disclosed several different types of plastic fasteners (also commonly referred to in the art as plastic attachments). Each plastic fastener described in the patent is manufactured in an H-shaped configuration, with two shortened parallel cross-bars, or T-bars, being interconnected at their approximate midpoints by a thin, flexible filament which extends orthogonally therebetween. Each type of plastic fastener represented in the patent is shown as being fabricated as part of continuously connected ladder stock. In each instance, the ladder stock is formed from two elongated and continuous plastic side members, or rails, which are coupled together by a plurality of plastic cross-links, or filaments, the cross-links preferably being equidistantly spaced.
Continuously connected ladder stock may be made by various different methods. One such method comprises extruding a continuous strip of plastic and then punching out or forming apertures in the strip in such a way as to leave only the side members and the cross-links in the strip. Another method comprises injection molding two or more separate lengths of the fastener stock and then joining together the lengths by applying heat to weld the respective side members together. Neither of these two methods has received much, if any, commercial use in the manufacturing of continuously connected ladder stock.
Still another method for manufacturing continuously connected ladder stock is described in U.S. Pat. No. 4,462,784, inventor Russell, issued Jul. 31, 1984, which patent is incorporated herein by reference. According to this patent, continuously connected ladder stock is made by a rotary extrusion process that involves the use of a rotating molding wheel whose periphery is provided with molding cavities that are complementary in shape to the molded ladder stock. To form fasteners, plastic is extruded into the cavities of the molding wheel, and a knife in substantially elliptical contact with the wheel is used to skive excess plastic from the molding wheel, leaving plastic only in the molding cavities. Following molding, the filament portions of the fasteners are typically stretched.
After its manufacture, continuously connected ladder stock is commonly wound onto a reel, or spool, which is sized and shaped to hold a supply of ladder stock that includes approximately 25,000 fasteners. In this manner, the reel can be used by a machine to continuously dispense a large quantity of individual fasteners, as will be described in detail below. Either manually or with the aid of specifically designed devices, individual fasteners may be severed and dispensed from a supply of ladder stock to couple buttons to fabric, merchandising tags to articles of commerce, or, in general, any two desired articles. Ladder stock of the type described above is presently manufactured and sold by Avery Dennison Corporation of Pasadena, Calif. under the Plastic Staples and Elastic Staple™ lines of plastic fasteners.
Specifically designed devices for dispensing plastic fasteners are well known in the art. One well-known device for dispensing individual plastic fasteners from a reel of ladder-type fastener stock includes a pair of hollow needles which are adapted to penetrate through a particular item, a feed mechanism for advancing each rail of the supply of ladder stock into axial alignment behind the longitudinal bore defined by a corresponding hollow needle, a severing mechanism for severing a fastener to be dispensed through the pair of hollowed needles from the remainder of the ladder stock, and an ejection mechanism for ejecting the cross-bars of the severed fastener through the bores of the pair of hollowed needles and, in turn, through the particular item which is penetrated by the needles.
Continuously connected ladder stock of the type described above is commonly manufactured using a flexible plastic material, such as nylon, polypropylene, or polyurethane. Conventional ladder stock does not exhibit melting characteristics until exposed to temperatures greater than 210° C. For example, TEXIN® 255, a polyester-based thermoplastic polyurethane manufactured by Bayer MaterialScience LLC of Pittsburgh, Pa., is commonly used to manufacture ladder stock. It should be noted that TEXIN® 255 polyurethane begins to exhibit melting characteristics only when exposed to temperatures greater than 210° C.